No details here of your iPad model or currently installed version of iOS/iPadOS.
If the problem does not relate to the iPad lock-screen Passcode, have you perhaps set-up ScreenTime restrictions? If so, depending upon the configured settings, you may need to enter the ScreenTime Passcode.
Settings > Screen Time > Content & Privacy Restrictions
If this is the issue - and you have forgotten the ScreenTime Passcode - dependent upon the age/model of your iPad, the ScreenTime Passcode can be reset using one of the two procedures outlined within this link:
If you forgot your Screen Time passcode - Apple Support
The more recent iPadOS updates have introduced a new mechanism whereby a forgotten ScreenTime passcode can be reset without wiping the iPad.
To reset a forgotten ScreenTime passcode on older versions of iOS/iPadOS, the iPad must be reset “as new”, losing all locally stored data. In this situation, you’ll not be able to restore your data from an iCloud or iTunes backup - as the forgotten passcode is integral to the backup.
I hope this information and explanation is helpful to you. If you have a different issue, we’ll need more specific information.
